[Numpy-discussion] question about ufuncs

Darren Dale dsdale24@gmail....
Fri Feb 6 17:11:10 CST 2009


On Fri, Feb 6, 2009 at 5:18 PM, Pierre GM <pgmdevlist@gmail.com> wrote:

>
> On Feb 6, 2009, at 4:25 PM, Darren Dale wrote:
>
> >
> > I've been looking at how ma implements things like multiply() and
> > MaskedArray.__mul__. I'm surprised that MaskedArray.__mul__ actually
> > calls ma.multiply() rather than calling
> > super(MaskedArray,self).__mul__().
>
> There's some under-the-hood machinery to deal with the data, and we
> need to be able to manipulate it *before* the operation takes place.
> The super() approach calls __array_wrap__ on the result, so *after*
> the operation took place, and that's not what we wanted...
>

It looks like there are enough cases where manipulation needs to happen on
the way in that it might be useful to consider a mechanism for doing so. It
could avoid the need for lots of wrappers and decorators down the road.


>
> > Maybe that is the way ndarray does it, but I don't think this is the
> > right approach for my quantity subclasses. If I want to make a
> > MaskedQuantity (someday), MaskedQuantity.__mul__ should be calling
> > super(MaskedQuantity,self).__mul__(), not reimplementations of
> > numpy.multiply or ma.multiply, right?
>
> You'll end up calling ma.multiply anyway
> (super(MaskedQuantity,self).__mul__ will call MaskedArray.__mul__
> which calls ma.multiply... So yes, I think you can stick to the
> super() approach in your case
>
> >
> > There are some cases where the default numpy function expects
> > certain units on the way in, like the trig functions, which I think
> > would have to be reimplemented.
>
> And you can probably define a generic class to deal with that instead
> of reimplementing the functions individually (and we're back to the
> initial advice).
>
>
> > But aside from that, is there anything wrong with taking this
> > approach? It seems to allow quantities to integrate pretty well with
> > the numpy builtins.
>
> Go and try, the problems (if any) will show up...
>

Oh boy...
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